Electronic oven



Aug. 29. 1967 H. w. DEATON 3,339,054

ELECTRONIC OVEN Filed April 20, 1964 4 Sheets-Sheet l INVENTOR Homer [4/ Oeafon H/s A/fokney Aug. 29, 1967 w DEMON 3,339,054

ELECTRONIC OVEN Filed April 20, 1964 4 Sheets-Sheet 2 84 36 26 L o 20 {Q 86 Ber-* L 0 j 34 g A al 3 F '9 2 INVENTOR Homer WDea/on BY .c

His A f/orney Aug. 29, 1967 H. w. DEATON 3,339,054

I ELECTRONIC OVEN Filed April 20, 1964 4 Sheets-Sheet 3 F n ('5' L T BE 5 22 I p 3) 84 26 28 1Q es 3' 3 i F v 3 INVENTOR.

Homer W Bea/0n BY 5W His A horney Aug. 29, 1967 H. w. DEATON 3,339,054

ELECTRONIC OVEN Filed April 20, 1964 4 Sheets-Sheet 4 F g. 5 Q INVENTOR.

Homer W Bea/0n His Af/omey Unitcd States Patent C) 3,339,054 ELECTRONIC OVEN Homer W. Deaton, Centerville, Ohio, assignor to General Motors Corporation, Detroit, MiclL, a corporation of Delaware Filed Apr. 20, 1964, Ser. No. 360,980 14 Claims. (Cl. 219-1055) This invention relates to heating apparatus and more particularly to a microwave oven arrangement for treating foodstuffs and the like.

One problem in development of an efiicient microwave oven structure suitable for domestic use is that of producing a suitable optimum matching of the output energy from a microwave generator with the load to be treated in the oven structure. In certain present-day oven configurations the best potential matching is not always obtainable, particularly where the front to rear dimensions of the domestic appliance must fit in a limited space as, for example, built-in oven structures or free-standing ranges of the type set forth in copending application Ser. No. 19,082, filed Mar. 31, 1960, now Patent No. 3,157,176. In such cases, many of the energy distributing arrangements heretofore disclosed in the microwave oven art have required a modification of such conventional oven structure including, in many cases, that outer dimensions therein, such as their front to rear dimensions, be extended beyond limited space requirements.

An object of the present invention, therefore, is to improve the matching of a microwave energy source with a load to be treated thereby in conventional oven structures of the type having a limited front to rear dimension.

A further object of the present invention is to provide an improved microwave oven wherein a source of microwave energy having a predetermined radio frequency mode for treating a load in a first cavity is coupled to the load by an enclosure characterized by a long shallow vertical cross-sectional configuration in which the output antenna of the generator is located at one end thereof and in which an iris opening is located adjacent the opposite end in a wall between the coupling enclosure and the oven cavity for, directing microwave energy from the interior of the enclosure into the cavity.

A further object of the present invention is to improve matching of the output of a microwave generator with a predetermined load by the provision of a complex multiple mode load treating cavity associated with a complex mode coupling cavity characterized, by a horizontal planar configuration having approximately fifty percent of the area of the horizontal planar configuration of the load treating cavity and wherein an iris opening is provided between theenclosure and the cavity adjacent one endof the cavity for directing the complex multi-mode radio frequency pattern in the enclosure into the load treating cavity.

Another object of the invention is to improve microwave ovens by the provision of plural communicating enclosures having multi-mode microwave patterns therein wherein one of the enclosures receives the output antenna of a microwave generator and has a movable probe therein for calibrating the pattern in said one enclosure to produce a desired load treating characteristic in another of the enclosures.

A further object of the present invention is to improve the efliciency of operation of a microwave oven by the provision of a microwave pattern forming and transmitting arrangement including an enclosure supported only on the top surface of a microwave oven enclosure to receive the output antenna of a microwave generator having a predetermined radio frequency mode emitted therefrom wherein the enclosure is dimensioned to produce a complex multi-mode radio frequency pattern transmittable through an iris opening between the enclosure and the load treating oven and further including means for varying the directional transmission of the multi-mode pattern to effect a uniform microwave treatment of the load.

A still further object of the present invention is to provide an improved microwave oven arrangement including a microwave generator emitting a predetermined electromagnetic mode into an enclosure configured to produce a multi-mode radio frequency pattern which is directed into the oven or load treating cavity in a variable manner by means of a rotatable element located in an iris opening between the enclosure and the oven to effect 121 high degree of matching between generator output and Yet another object of the invention is to improve the operation of a microwave oven having a microwave generator and a radiant browning element by the provision of a control system having a timer including a single synchronous timing motor, and a selector switch means for operably associating the single timing motor and one or both of the wave generator and radiant browning element to effect joint microwave and browning of a predetermined load or single timed browning or single timed microwave cooking.

Yet another object of the invention is to include improved circuit means associable with a power circuit for a microwave oven or the like to prevent relay contact welding therein.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIGURE 1 is a view in front elevation of a conventional oven construction including the microwave cooking system of the present invention;

FIGURE 2 is an enlarged view in vertical section taken along the line 2-2 of FIGURE 1;

FIGURE 3 is a view in vertical section taken along line 3-3 of FIGURE 2;

FIGURE 4 is a view in horizontal section taken along the line 44 of FIGURE 3 and looking in the direction of the arrows;

FIGURE 5 is a view in horizontal section taken along the line 55 in FIGURE 3 looking in the direction of the arrows; and

FIGURE 6 is a diagrammatic view of the control circuitry of the present invention.

Referring now to the drawings and FIGURE 1, a builtin type cooking appliance 10 is illustrated, it being specifically set forth in copending application S.N. 19,082 filed Mar. 31, 1960 now Patent No. 3,157,176. For purposes of understanding the present invention, it is merely necessary to point out that the appliance 10 includes a conventional oven structure 12 enclosed by this same outer casing that encloses a smaller side oven structure 14 that has been modified to perform a microwave cooking operation in accordance with the principles of the present invention.

As illustrated in FIGURE 1, above the side-by-side ovens 12 and 14 is a control panel 16 that extends completely across the width of the appliance 10 and above the panel 16 is a vent opening 18 for the appliance 10.

Referring now more particularly to the oven 14, as best illustrated in FIGURES 2 through 5, an arrangement is illustrated wherein an outer shell or cabinet 20 is located in spaced surrounding relationship with an oven enclosure 22 having a rear wall 26, side walls 28, 30, bottom wall 31, and a top surface 32 to form in cooperation with the outer shell 20 a surrounding air passageway 33 for cooling the microwave oven structure. The air for cooling passes into passageway 33 from opening 34 in the front of the oven 14. It then passes across the top of enclosure 22 through an opening 35 in the top surface 32 and then from the enclosure 22 through an exit opening 37 in the front top thereof and an outlet opening 39 in the upper front of oven 14.

The interior space, or cavity, 36 formed by the walls of the microwave oven is accessible through an opening 38 formed by the outer casing 20 which is, in turn, closed by a door closure element 40 including a suitable microwave energy shield as is well known by those skilled in the art. In the illustrated arrangement, above the door 40 is a transversely directed light enclosure 42 including means therein, for example, an elongated fluorescent bulb 44 for illuminating the front of the appliance 10. For purposes of simplifying the present disclosure, the space immediately behind the cooking panel 16 and Ventilator opening 18 is left blank, with it being understood that a power supply and venting arrangement is included therein.

Now, in accordance with certain of the principles of the present invention, an arrangement is provided in association with the oven cavity 36 to more efficiently match the output of a microwave generator unit, or magnetron, 46 with a load to be treated within the cavity 36. More particularly, this improved arrangement includes an enclosure 48 located in overlying relationship with substantially all of the upper surface 32 of the oven cavity 36 with the enclosure 48 having a continuous, outwardly inclined, side wall 50 formed substantially in a horseshoelike configuration as best shown in FIGURE 4. In the illustrated embodiment the upper surface 52 of the enclosure 48 has an opening 54 therein through which a dome protected output antenna 56 of the magnetron 46 is directed interiorly of the enclosure 48 at a point where the center line thereof is located a mean distance three and five-eighths inches from the rear segment of the wall 50. The part of the side wall 50 that immediately surrounds the antenna 56 includes a plurality of openings 58 therein through which the circulating cooling air passes from the duct 33, from thence it passes through theiris opening 35, oven cavity 36 and out of the oven through openings 37, 39. In the illustrated arrangement, the center line of the iris opening 35 is located a distance six and one-sixteenth inches from the center line of the antenna 56.

One characteristic of the enclosure 48 is that certain of its dimensions are substantially greater than the wave length of the primary mode emitted by the magnetron unit 46. In one working embodiment of the invention, the enclosure 48, which can also be characterized as an energy transmitting compartment, has a substantial length and shallow depth in vertical section, as best seen in FIGURE 2. Moreover, the total horizontal planar area of the enclosure 48 is in the range of fifty to fifty-five percent of the horizontal planar area of the oven interior 36. By virtue of this arrangement, it has been found that when a predetermined electromagnetic mode is emitted from the antenna 56 into the interior 60 of the enclosure 48, as for example, a TE mode, the enclosure 48 will produce a relatively complex multiple mode microwave pattern therein for transmission interiorly of the oven cavity 36 which mode pattern is highly effective in producing an optimum match between the output of the magnetron 46 and various type loads to be treated in the oven 36. One advantage of'such optimum matching is that the magnetron 46 can be operated in a lower current consumption range to improve its life expectancy.

Another feature of the enclosure configuration is that it produces this multi-mode, highly eflicient, matching arrangement without interfering with the oven and ventilating ductwork as present in conventional built-in oven type structures wherein the front to rear depth and vertical outside dimensions may be limited.

In order to further improve the matching characteristics of the present invention, certain means can be present in the multiple mode energy containing enclosure 48 for varying the direction thereof through the iris opening 62 into the oven cavity 36. One such device for obtaining such variable energy direction is the use of a stirring assembly 62 including a rotatable stirrer 64 having blades 66, 68 thereon connected to a motor shaft 70 of an electric motor 72 wherein the blades 66, 68 are concentrically arranged with respect to the opening 35 so that the outer ends thereon are located immediately adjacent but within the edge of the opening 62. In accordance with certain other of the principles of the present invention, the blades 66, 68 are pitched or turned about their longitudinal axis to produce a load effect on the induction motor 72 to reduce the speed thereof below the synchronous speed of the motor to thereby change the frequency relationship between the magnetron output and the speed of rotation of the blades for effecting a variable directional input of multiple mode energy pattern produced by the emitted microwave energy from the magnetrons as modified by the enclosure 48.

In certain cooking applications it has been found that a wide range of different foodstuffs can be uniformly treated while retaining desirable matching characteristics in the oven without providing an input direction varying component such as the stirring assembly 62. In such a case, however, it is desirable to calibrate the mode pattern characteristics of the enclosure 48 to effect a desirable input of the pattern through the iris opening 35 into the oven cavity 36. Accordingly, another feature of the invention is the provision of a tuning probe 74 located within the enclosure interior 60 at a point approximately two and one-eighth inches from the center line of the output antenna 56. The probe 74 is representatively shown as an L-shaped member which has an upwardly directed portion 76 and a base portion 77 supported on the outer surface of the top wall 32. A pair of spaced stud elements 78 depend from the base 77 to extend through spaced openings 80. 82 in the top wall 32 to serve as means for slidably guiding the probe with respect to the center line of the output antenna 56. By virtue of the above-described arrangement, a movement of the probe with respect to the output antenna will effect a desired calibration of the microwave oven whereby the multi-mode pattern in the enclosure 48 will be most suited for a particular oven enclosure associated therewith. Once the probe is so located, it is releasably held in place by nut elements 83 threadably received by studs 78.

Another feature of the illustrated tuning probe arrangement is that it can produce variable directional input of the multi-mode pattern in enclosure 48 similar to that produced by the stirring assembly 62. More particularly, if the tuning probe 74 is connected to a suitable oscillating drive arrangement to be moved about the illustrated location approximately one-sixteenth inch on either side thereof, it has been found that a TB mode emitted from the magnetron 46 will be directed through the iris opening '35 to assure a uniform treatment of the load in the oven cavity 36 without adversely affecting the optimum matching characteristics produced by the multi-mode energy pattern in enclosure 48.

An electrical resistance element 88 is supported within the cavity 36 adjacent the upper level thereof and a pair of lights 90 project from the rear wall 36 of the oven above the resistance element 88 for illuminating the interior thereof, with the pair of lights 90 having conventional shields thereon for protecting against destruction produced 'by the introduction of microwave energy interior of the cavity 36. Between the lights 90 and the resistance element 88 is a glass plate 92 for shielding the stirrer 64 from food splatter and the like from the cavity 36. The shield 92 is supported on suitable rack means 94 and in one working embodiment was constructed from a oneeighth inch window glass material which is impervious to food splatter and a free conductor of microwave energy. Vertically arranged pairs of racks 84, 86 are supported on the sides 28, 30 of the oven enclosure 22 so that the load to be treated within the cavity 36 can be moved with respect to the resistance element 88 to obtain varying browning effect.

Another feature of the invention is the manner in which the microwave generator 46 and the electrical resistance element 88 are controlled to produce a wide range of combination cooking effects. As is well known to those skilled in the art, while microwave cooking is suitable for raising the interior temperature of foodstuffs to a desired level, it fails to produce a desired aesthetically pleasing browned appearance. Hence, such cooking must be supplemented by a source of radiant heat such as the electrical resistance element 88 in FIGURES 3 and 5. The combination cooking effects obtainable by each source of energy is empirically determined by trial and error cooking of a wide range of food stuffs. In order to obtain a desired wide range of cooking effects in the present invention, a control system is illustrated that includes a manually controllable timer knob 96 that is presettable into one of a plurality of positions and can be pushed in toward the face of the panel 16 to serve as a momentary push actuator for a momentary switch element. Adjacent to the knob 96 is located a selector switch 98 for an on and off position for controlling energization of the resistance heater'88. In addition to the knobs 96, 98 is a power switch 100 for selecting low and high ranges of energization of the magnetron or microwave generator 46 as is well known to those skilled in the art. It will be understood that other suitable controls will be present on the control panel 16 for effecting a controlling operation of the conventional oven 12 of the appliance 10.

I With reference to the control circuit illustrated in FIGURE 6, when an electronic cooking operation is to be commenced, the door 14 is moved into a closed position wherein a door switch 102 is closed along with a safety switch 104, both switches being included in a circuit connected across lines L L of a conventional three-wire power supply including the lines L L and a line N. Following door closure the timer 96 is moved into a desired rotated position to close a pair of timer switches 108 in parallel conductors 109, 111 connected to L and to, close a pair of timer switches 110 in parallel conductors 112 and 113 connected to line L' fln a typical cooking operation, once the switches 108, 110 are closed an initial microwave cooking warm-up occurs that includes closing a time delay switch 114 by a time delay mechanism 115, electrically connected across lines N, L by a conductor 116, Following or during movement of the timer 96 into a rotated position and closure of the time delay switch to effect microwave energization, the timer knob 96 is pushed inwardly to close a momentary switch 118. Closure of time delay switch 114 and momentary switch 118 completes a relay circuit from lines L through switch 108, conductor 111, switch 118, a resistor 120, fuse 122, a safety interlock 124, switches 102, 104, a high temperature magnetron cut-out element 126, a relay coil 128, switch 114, conductor 113, switch 110 to line L "Once the relay coil 128 is energized, relay switches 130, 132 are closed whereby a timing circuit is completed from L through switch 108, conductor 111, relay switch 132, synchronous timer motor 134 and conductor 136 to N. Closure of the switch 130 completes a power circuit including line L switch 108, conductor 111, relay switch 130, fuse 122, interlock 124, switches 104, 102, the input terminal of a primary coil 138 and thence through the output terminal thereof through a selector switch 142 movable into high and low power positions upon rotation ofknob.100.

The primary coil 138 is only one portion of a typical microwave oven power supply 144 of a type commonly known to those skilled in the art. Such a power supply 144 includes an output circuit 146 for energizing the magnetron and another output circuit 148 for energizing the motor 72 for operating the stirrer assembly 62.

If it is desired to follow an initial microwave cooking cycle with a browning cycle of operation, a user moves the selector knob 98 into an on position. This closes one of a pair of selector switches 150 in the conductor 109 and the other of the switches 150 ina conductor 152 between conductor 111 and conductor 136 whereby a browning element circuit 154 is closed between lines L and L for energizing the electrical resistance element 88. Typically, the adjustment of the selector switch 98 may be effected before the complete electronic cooking cycle has been timed out. In this case the resistance element 88 will be energized for a predetermined remainder of the complete electronic cooking cycle and both the magnetron 46 and resistance element 88 will be timed out together when the timer switches 198, 110 are opened by timer 96.

In some cases it may be desirable to operate the oven 14 solely as a radiant energy heating device. In this case a user rotates the knob 96 into a rotated position an'd turns the knob 98 into an on position whereby the timer circuit is completed between lines L and N through timer motor 134 and the resistance element energization circuit 154 is completed between lines L and L The power supply for the magnetron 46 is de-energized, however, since the momentary push button switch 118 has not been operated. Accordingly, a timed control of electrical resistance heating only is effected. In light of the above remarks, it will be appreciated by those skilled in the art that the illustrated control circuit can be utilized to concurrently control both sources of energy in the oven or to separately control one or the other of the sources of energy, depending upon the desires of the individual user. Furthermore, this wide range of control flexibility is accomplished by a low-cost, reliable arrangement of components.

One problem that has existed in the control and power circuit for microwave cooking is due to the residual magnetism present in the power transformer components thereof following energization thereof. Suoh residual magnetism will, upon re-energization of the transformer, produce a high transient curre'nt that is capable of welding many control switch contacts together. In the circuit illustrated in FIGURE 6, the coil 138 constitutes the primary side of such a transformer. Hence, in the illustrated arrangement, following de-energization of the power supply 144 by opening the timer switches 108, 110, a resdiual magnetism is built up that upon re-energization Otf the power supply will cause a high transient current to ensue in the power circuit between lines L and L which can weld. together contacts in switch 130.

Accordingly, another feature of the invention is the provision of a compensating circuit in association with the coil 138 to prevent such a high transient current from passing through relay switch 130. The compensating circuit, more particularly, includes the momentary push switch 118 and the resistor in parallel with the relay switch 130. Upon re-energization of the circuit following a previous microwave cooking operation, momentary closure of switch 118 to complete the circuit across the primary coil 138 will include the resistor 120 in series with the relay coil 128. The resistor 120 acts to limit the initial current flow to the transformer coil 138. "Dhis effectively chokes down the high transient current that would otherwise ensue because of the residual magnetism in the transformer. The limiting effect of the resistor 120 continues until the voltage across the transformer has increased sufficiently to demagnetize the transformer core. The reduced current flow that passes through the relay coil 128 before such demagnetization is not suificient to close the relay switch 130. A momentary closure of the switch 118 is sufficient to accomplish demagnetization of the transformer core and once this occurs, a sufficient voltage occurs across the relay coil 128 to produce a current flow therethrough sufficient to actuate the relay switches 130, 132 into a closed position to complete the power circuit and timer circuit of FIGURE 6. These circuits, however, are not completed until the high transient current condition has been eliminated. Hence, the contacts of switch 130 do not Weld together during their controlling operation.

It will be appreciated in view of the above remarks that applicant has first of all developed a microwave oven configured to improve its efficiency of operation and especially suited for association with oven units having critical front to rear and vertical dimensional limitations. Additionally, the arrangement includes an economical control for carrying out a wide range of combination or single radiant and microwave cooking operations and wherein various modifications are included in a conventional microwave control circuit to prevent contact destruction and other undesirable side effects.

Wlhile the embodiments of the present invention as herein disclosed constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In a microwave oven, the combination of a food preparation enclosure having a bottom wall, side walls and a rear wall, a source of microwave energy, an enclosure located between said source of energy and said food preparation cavity having a planar configuration of a generally horseshoe shape, said enclosure being separated from said foo-d preparation cavity by a common divider wall, said microwave energy generating means being located adjacent the small radius end of said horseshoe shaped enclosure for generating a predetermined radio frequency mode into said enclosure, said enclosure having certain of its dimensions substantially greater than the wave length of the microwave energy radio frequency mode for producing a complex multi-mode radio frequency pattern to improve oven efiiciency, means forming an iris opening in said common wall for directing said multi mode radio frequency pattern into said food preparation cavity, and means in said oven cavity including a rotary stirrer element for producing a further mixing of the radio frequency modes to produce a still further variance of mode pattern in said oven cavity for an improved uniform microwave treatment of the load in the oven cavity.

2. In a microwave oven, means forming a load cavity, a source of microwave energy for transmitting a predetermined electromagentic energy mode, an enclosure for receiving the predetermined electromagnetic mode and producing a complex multi-mode radio frequency pattern, means forming an iris opening between said load cavity and said multi-mode containing enclosure, means for varying the directional input of said multimode cavity through said iris opening into said load cavity including a stirrer paddle having the outer ends thereof located within said iris opening, said paddle having the vanes thereon pitched to produce a substantial loading on said induction electric motor for reducing the speed thereof below its synchronous speed to vary the frequency relationship between the source of microwave energy and said motor.

3. In a microwave oven assembly having a limited outer front to rear dimension, a first load cavity having a front opening therein, door closure means for said opening, means forming an air circulation duct surrounding said first cavity formed in part by the outer shell of said oven at the bottom and rear thereof, a source of microwave energy emitting a predetermined electromagnetic radio frequency mode, means forming an enclosure surrounding the output antenna of said generator, said enclosure in part being formed by the upper surface of said first cavity and having a relatively long shallow vertical cross-sectional configuration for coupling said source of microwave energy to said first cavity without affecting the front to rear dimensions of the oven structure, said enclosure being configured with respect to the output of said generator to producea highly complex multimode radio frequency pattern therein to improve match-- ing of load to source of microwave energy, an iris opening in said upper surface for directing the multi-rnode pattern into said first cavity, and means for variably directing said multi-mode wave pattern toward a load insaid first cavity, said means for maximizing such matching including a rotatable stirrer device concentrically arranged with respect to said iris opening interiorly of said enclosure for producing a varying directional input of said multi-mode pattern into said first enclosure.

4. In the combination of claim 3, said variable pattern directing means including an oscillating member movable between the output antenna of the generator and the rear wall of said enclosure to thereby producea variable deflection of the multi-mode pattern of the enclosure through said iris opening.

5. In the combination of claim 3, said enclosure having a plurality of openings adjacent the antenna enclosing the end thereof for effecting a desired cooling of the interior of said enclosure.

6. In the combination of claim 3, said multi-mode producing enclosure having a horizontal cross-sectional configuration approximately fifty percent of the horizontal cross-sectional configuration of said load cavity.

7. In a microwave oven, the combination of means forming a load containing cavity, a source of microwave energy emitting a predetermined radio frequency mode, an enclosure communicating with said load containing cavity, said enclosure receiving said emitted microwave energy and being dimensioned to produce a complex multi-mode radio frequency pattern therein, and means within said enclosure movable with respect to the output antenna of the source of microwave energy to calibrate the multi-mode pattern in said enclosure with the load cavity.

8. In the combination of claim 7, means for calibrating said enclosure to said load cavity including a tuning probe member movable with respect to the center line of the output antenna of said source for effecting avariation of the multi-mode pattern in said enclosure for optimizing matching of the microwave generator to a wide range of foodstuffs to be treated in the load cavity.

9. In the combination of claim 7, said probe having an L-shape with an upstanding portion and a base portion, said base portion having depending means thereon coacting with said load cavity for slidably guiding said probe into varying locations with respect to the center line of said source.

10. In a microwave oven, the combination of a food preparation enclosure having a bottom wall, side walls and a rear wall, a source of microwave energy, an enclosure located between said source of energy and said food preparation cavity having a planar configuration of a generally horseshoe shape, said enclosure being separated from said food preparation cavity by a common divider wall, said microwave energy generating means being located adjacent the small radius end of said horseshoe-shaped enclosure for generating a predetermined radio frequency mode into said enclosure, said enclosure having certain dimensions thereof substantially greater than the wave length of the microwave energy radio frequency mode for producing a complex multi-moderadio frequency pattern to improve load to microwave source matching, means forming an iris opening in 'said common wall for directing said multi-mode radio frequency pattern into said food preparation cavity, and probe means within said multi-mode generating enclosure, said probe means being movable relative to said source of microwave energy to calibrate'the multi-mode producing enclosure to its associated food preparation wave energy and being dimensioned to produce a compleX multi-mode radio frequency pattern therein to improve matching of load to said source of microwave energy, current controlling electrical circuit for supplying power to said source of microwave energy including a transformer coil having a residual magnetism following energization thereof, a relay coil in parallel with said transformer coi'l, a relay switch having a pair of contacts serially arranged with said parallel relay coil and transformer coil, and means for preventing a high transient current through said relay contacts upon re-energization of a transformer coil including momentary push switch means and a resistor element for reducing current flow through said relay coil until residual magnetism has decayed in said transformer coil, said relay coil responding to an increased voltage thereacross upon decay of such residual magnetism to effect closure of said relay contacts.

12. A current controlling electrical circuit comprising a transformer coil having a residual magnetism following energization thereof, a relay coil in parallel With said transformer coil, a relay switch having a pair of contacts serially arranged with said parallel relay coil and transformer coil, and means for preventing a high transient current through said relay contacts upon re-energization of a transformer coil including switch means and a resistor element for reducing current flow through said relay coil until residual magnetism has decayed in said transformer coil, said relay coil responding to an increased voltage thereacross upon decay of such residual magnetism to effect closure of said re'lay cont-acts.

13. In a microwave oven structure, means forming a load cavity, a source of microwave energy for treating said load and an electrical resistance element for browning said load, a source of power for energizing said microwave generator and said electrical resistance element, timer control means for regulating the period of energization of said microwave generator, a selector switch for coupling said electrical resistance element to said timer control for said microwave generator for concurrently timing out the generator and resistance element for a predetermined microwave treating period, and means for selectively disconnecting said microwave generator from its timer control including a momentary push control knob and switch effective to disconnect the microwave generator from the source of power during operation of its timer means whereby said electrical resistance element can be timed independently of said microwave generator if desired.

14. In a microwave oven structure, means forming a load cavity, a source of microwave energy for treating said load and an electrical resistance element for browning said load, a source of power for energizing said microwave generator and said electrical resistance element, timer control means including a single induction electric motor energizab'le by said power source for regulating the period of energization of said microwave generator, a selector switch for coupling said resistance element to the timer control for said microwave generator for concurrently timing out the generator and resistance element for a predetermined microwave treating period, and means for selectively disconnecting said microwave generator from its timer control whereby said browning element can be timed independently of said microwave generator if desired.

References Cited printed April 1962.

RICHARD M. WOOD, Primary Examiner. ANTHONY BARTIS, Examiner. L. H. BENDER, Assistant Examiner, 

13. IN A MICROWAVE OVEN STRUCTURE, MEANS FORMING A LOAD CAVITY, A SOURCE OF MICROWAVE ENERGY FOR TREATING SAID LOAD AND AN ELECTRICAL RESISTANCE ELEMENT FOR BROWNING SAID LOAD, A SOURCE OF POWER FOR ENERGIZING SAID MICROWAVE GENERATOR AND SAID ELECTRICAL RESISTANCE ELEMENT, TIMER CONTROL MEANS FOR REGULATING THE PERIOD OF ENERGIZATION OF SAID MICROWAVE GENERATOR, A SELECTOR SWITCH FOR COUPLING SAID ELECTRICAL RESISTANCE ELEMENT TO SAID TIMER CONTROL FOR SAID MICROWAVE GENERATOR FOR CONCURRENTLY TIMING OUT THE GENERATOR AND RESISTANCE ELEMENT FOR A PREDETERMINED MICROWAVE TREATING PERIOD, AND MEANS FOR SELECTIVELY DISCONNECTING SAID MICROWAVE GENERATOR FROM ITS TIMER CONTROL INCLUDING A MOMEMTARY PUSH CONTROL KNOB AND SWITCH EFFECTIVE TO DISCONNECT THE MICROWAVE GENERATOR FROM THE SOURCE OF POWER DURING OPERATION OF ITS TIMER MEANS WHEREBY SAID ELECTRICAL RESISTANCE ELEMENT CAN BE TIMED INDEPENDENTLY OF SAID MICROWAVE GENERATOR IF DESIRED. 